Place the butter in a saucepan and melt over medium heat. Swirl the pan and allow the butter to bubble and foam slightly. Continue browning the butter until it begins to smell nutty and it turns a dark golden brown. Remove it from the heat and allow the butter to cool to room temperature.,Sift together the flour, salt, baking soda and cornstarch. Set the dried ingredients aside.,Place the browned butter and both sugars into the bowl of a stand mixer. Beat for about 1-2 minutes. Add in the egg, egg yolk and vanilla extract until combined. On low, slowly add in the dry ingredients until just combined. Using a wooden spoon, stir in the chocolate chunks and toffee bits.,Chill the cookie dough for about 1 hour.,Preheat the oven to 325°F. Line baking sheets with parchment paper or Silpat mats.,______,Bake for about 15 minutes until the edges of the cookies begin to turn golden brown and have set. Allow the cookies to cool on the baking sheets for 5 minutes before transferring to a wire rack to cool completely.